Which number replaces the question mark?

Question

Answer 1

1 * 1 = 1 * 2 = 2
2 * 2 =4 * 2 = 8
3 * 3 = 9 * 2 = 18
4 * 4 = 16 * 2 = 32
5 * 5 = 25 * 2 = 50
6 * 6 = 36 * 2 = 72
7 * 7 = 49 * 2 = 98
8 * 8 = 64 * 2 = 128
9 * 9 = 81 * 2 = 162.

Answer is 72